Network Device Configured to Track Multicast Receivers

1. An apparatus comprising: a first network device adapted for communication with one or more other network devices; the first network device comprising a processor coupled to a memory; the first network device being configured: to originate a first route identifying a first tunnel for carrying traffic for a multicast; to originate a second route specifying a leaf information requirement for the multicast but not initially identifying any tunnel for carrying traffic for the multicast; and to track a plurality of receivers of the multicast based at least in part on leaf information received from the multicast receivers responsive to the specified leaf information requirement of the second route; wherein the first route comprises an inclusive route having a first tunnel attribute that identifies the first tunnel as an inclusive tunnel for the multicast and the second route comprises a selective route having a second tunnel attribute configured to indicate that it carries no tunnel information; wherein the second tunnel attribute of the selective route is configured to indicate that it carries no tunnel information by setting a tunnel type field of the second tunnel attribute to a predetermined value; and wherein the first network device is further configured to switch traffic for the multicast from the first tunnel identified by the first route to a second tunnel by updating the second route to identify the second tunnel for carrying traffic for the multicast.

2. The apparatus of claim 1 wherein the specified leaf information requirement of the second route is established by setting a leaf information field of the second tunnel attribute of the second route to a predetermined value.

3. The apparatus of claim 2 wherein the leaf information field of the second tunnel attribute of the second route comprises a leaf information required flag that is set to a logic one value to indicate the specified leaf information requirement.

4. The apparatus of claim 1 wherein the leaf information received from a given one of the multicast receivers responsive to the specified leaf information requirement of the second route comprises information associated with a leaf auto-discovery route originated by the given multicast receiver responsive to the specified leaf information requirement.

5. The apparatus of claim 4 wherein the specified leaf information requirement provides an indication to the given multicast receiver that it should not establish a forwarding path to the second route.

6. The apparatus of claim 1 wherein the first network device is further configured to switch traffic for the multicast from the second tunnel back to the tunnel identified by the first route by updating the second route so as to no longer identify the second tunnel for carrying traffic for the multicast.

7. The apparatus of claim 1 wherein the first network device is further configured to disable tracking of the multicast receivers by withdrawing the second route.

8. A communication network comprising the apparatus of claim 1 .

9. A method comprising: originating a first route identifying a first tunnel for carrying traffic for a multicast; originating a second route specifying a leaf information requirement for the multicast but not initially identifying any tunnel for carrying traffic for the multicast; and tracking a plurality of receivers of the multicast based at least in part on leaf information received from the multicast receivers responsive to the specified leaf information requirement of the second route; wherein the originating first and second routes and the tracking are performed by a network device; wherein the first route comprises an inclusive route having a first tunnel attribute that identifies the first tunnel as an inclusive tunnel for the multicast and the second route comprises a selective route having a second tunnel attribute configured to indicate that it carries no tunnel information; wherein the second tunnel attribute of the selective route is configured to indicate that it carries no tunnel information by setting a tunnel type field of the second tunnel attribute to a predetermined value; and wherein the method further comprises switching traffic for the multicast from the first tunnel identified by the first route to a second tunnel by updating the second route to identify the second tunnel for carrying traffic for the multicast.

10. The method of claim 9 further comprising disabling the tracking of the multicast receivers by withdrawing the second route.

11. An article of manufacture comprising a non-transitory processor-readable storage medium having embodied therein executable program code that when executed by a network device causes the network device: to originate a first route identifying a first tunnel for carrying traffic for a multicast; to originate a second route specifying a leaf information requirement for the multicast but not initially identifying any tunnel for carrying traffic for the multicast; and to track a plurality of receivers of the multicast based at least in part on leaf information received from the multicast receivers responsive to the specified leaf information requirement of the second route; wherein the first route comprises an inclusive route having a first tunnel attribute that identifies the first tunnel as an inclusive tunnel for the multicast and the second route comprises a selective route having a second tunnel attribute configured to indicate that it carries no tunnel information; wherein the second tunnel attribute of the selective route is configured to indicate that it carries no tunnel information by setting a tunnel type field of the second tunnel attribute to a predetermined value; and wherein the program code when executed by the network device further causes the network device to switch traffic for the multicast from the first tunnel identified by the first route to a second tunnel by updating the second route to identify the second tunnel for carrying traffic for the multicast.

12. The article of claim 11 wherein the program code when executed by the network device further causes the network device to disable the tracking of the multicast receivers by withdrawing the second route.

13. An apparatus comprising: a first network device adapted for communication with one or more other network devices; the first network device comprising a processor coupled to a memory; the first network device being configured: to join a multicast for which a first route has been originated identifying a first tunnel for carrying traffic for the multicast; to obtain a leaf information requirement specified by a second route originated for the multicast but not initially identifying any tunnel for carrying traffic for the multicast; and to provide leaf information responsive to the specified leaf information requirement of the second route for use in multicast receiver tracking; wherein the first route comprises an inclusive route having a first tunnel attribute that identifies the first tunnel as an inclusive tunnel for the multicast and the second route comprises a selective route having a second tunnel attribute configured to indicate that it carries no tunnel information; wherein the second tunnel attribute of the selective route is configured to indicate that it carries no tunnel information by setting a tunnel type field of the second tunnel attribute to a predetermined value; and wherein the first network device is further configured to switch from the first tunnel identified by the first route to a second tunnel responsive to updating of the second route to identify the second tunnel for carrying traffic for the multicast.

14. The apparatus of claim 13 wherein the first network device is further configured to switch from the second tunnel back to the first tunnel identified by the first route responsive to further updating of the second route to no longer identify the second tunnel for carrying traffic for the multicast.

15. A method comprising: joining a multicast for which a first route has been originated identifying a first tunnel for carrying traffic for the multicast; obtaining a leaf information requirement specified by a second route originated for the multicast but not initially identifying any tunnel for carrying traffic for the multicast; and providing leaf information responsive to the specified leaf information requirement of the second route for use in multicast receiver tracking; wherein the joining, obtaining and providing are performed by a network device; wherein the first route comprises an inclusive route having a first tunnel attribute that identifies the first tunnel as an inclusive tunnel for the multicast and the second route comprises a selective route having a second tunnel attribute configured to indicate that it carries no tunnel information; wherein the second tunnel attribute of the selective route is configured to indicate that it carries no tunnel information by setting a tunnel type field of the second tunnel attribute to a predetermined value; and wherein the method further comprises switching from the first tunnel identified by the first route to a second tunnel responsive to updating of the second route to identify the second tunnel for carrying traffic for the multicast.

16. The method of claim 15 wherein providing leaf information responsive to the specified leaf information requirement comprises originating a leaf auto-discovery route responsive to the specified leaf information requirement.

17. The method of claim 16 further comprising: receiving a prune message relating to the multicast; and withdrawing the leaf auto-discovery route responsive to the prune message.

18. The method of claim 15 wherein providing leaf information responsive to the specified leaf information requirement comprises providing the leaf information without establishing a forwarding path to the second route.

19. The method of claim 15 further comprising switching from the second tunnel back to the first tunnel identified by the first route responsive to further updating of the second route to no longer identify the second tunnel for carrying traffic for the multicast.

20. An article of manufacture comprising a non-transitory processor-readable storage medium having embodied therein executable program code that when executed by a network device causes the network device: to join a multicast for which a first route has been originated identifying a first tunnel for carrying traffic for the multicast; to obtain a leaf information requirement specified by a second route originated for the multicast but not initially identifying any tunnel for carrying traffic for the multicast; and to provide leaf information responsive to the specified leaf information requirement of the second route for use in multicast receiver tracking; wherein the first route comprises an inclusive route having a first tunnel attribute that identifies the first tunnel as an inclusive tunnel for the multicast and the second route comprises a selective route having a second tunnel attribute configured to indicate that it carries no tunnel information; wherein the second tunnel attribute of the selective route is configured to indicate that it carries no tunnel information by setting a tunnel type field of the second tunnel attribute to a predetermined value; and wherein the program code when executed by the network device further causes the network device to switch from the first tunnel identified by the first route to a second tunnel responsive to updating of the second route to identify the second tunnel for carrying traffic for the multicast.

21. The article of claim 20 wherein the program code when executed by the network device further causes the network device to switch from the second tunnel back to the first tunnel identified by the first route responsive to further updating of the second route to no longer identify the second tunnel for carrying traffic for the multicast.